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What do the saw marks on boards tell me?

Started by NotEnoughTime, March 08, 2020, 07:34:20 PM

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NotEnoughTime

I've been using a non-hydraulic bandmill for the past 1.5 years, learning my way (and avoiding mistakes) by reading old forum posts.  I'm looking for some wisdom from the experienced sawyers who may be 'milling around' on something that's been nagging me.

The first few inches of each board show a pattern:


  • A smooth start (about the width of the saw blade)
  • An angled pattern (which varies from an inch or so to several inches)
  • A stable pattern of straight saw-marks (which I suspect match the welded spot on the blade)

What should I glean from this?   I've noticed if #3 marks are angled, and not straight, I need to adjust the blade guides.   But why does #2 vary in width?   Can it be eliminated?   What can I learn from it?

HM130 with extended 18' trailer + boat winch, homemade log arch, oak ramps, cant hook and lots of leverage.

btulloh

(Man! today seems to have gone by really quickly!  ;) )

If I'm understanding your description it sounds like what I get if my drive  belt is slipping, either from lack of tension (stretching) or pitch/sawdust buildup.

Unless there's a bad weld, it shouldn't cause any marks.  A proper weld will be smooth on both sides and the back.  Nothing to leave a mark.  I did get a couple funky welds in the pack of 10 blades I got with my HM126.  Not sure who's making the blades for Woodland Mills, but maybe they switched by now.  (I don't think it's a Lennox problem - it's a weld problem.)  I've been using nothing but Kasco blades after that original box of Lennox 10's and don't ever see a bad weld, although it's always possible that one could sneak through QC.

In any event, if the drive belt tension is ok and there's no belt slippage from another issue, you should not see those marks.  Assuming proper blade tension of course.  (I've found that I need just a bit more tension than what they call for, BTW.)

(how 'bout a picture?)

As for belts, I think I'm going to order some from WoodMizer to try.  None of the belts I've sourced locally or ordered have seemed to last very long.  It could be that none of those were spec'd for back idler application.  I hear a lot of good things about the Woodmizer belts and they seem to hold up a LOT longer than mine do.
HM126

NotEnoughTime

Ahh... I see my two photo illustrations didn't post.  Adding them now.

 

 
HM130 with extended 18' trailer + boat winch, homemade log arch, oak ramps, cant hook and lots of leverage.

WV Sawmiller

I'd guess you have a tooth out of set. Swap blades and see if it goes away or changes. Also see what happens when you saw faster. Let us know what you find. Welcome to the FF.
Howard Green
WM LT35HDG25(2015) , 2011 4WD F150 Ford Lariat PU, Kawasaki 650 ATV, Stihl 440 Chainsaw, homemade logging arch (w/custom built rear log dolly), JD 750 w/4' wide Bushhog brand FEL

Dad always said "You can shear a sheep a bunch of times but you can only skin him once

Southside

Yup - that's a tooth that got knocked.  The washboard that is at the beginning of the cut is a sign of sawing too slow, it's often seen at the beginning of a cut as typically you don't enter the log at a full clip.  Some profiles are more prone to showing it than others, but yes, change bands and see what you get for results. 
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YellowHammer

I agree, a tooth (looks like one badly, two other not too bad) out of set for the board length pattern.  

I always attributed the rolling pattern to band resonance, or band bounce, which can be caused by a number of things including sawdust buildup under the band wheels, too slow of feed rate and a sharp band.  Mathematically, the way to get out of resonance is to change a variable, and the easiest thing to change is to speed up the feed and put more load on the band.  The rolling washboard pattern will go away.  It will come back if you slow down.  
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

NotEnoughTime

Adding some information:  I was using Woodmizer 10 degree bands (a bit thicker than the Lennox blades I started with).  I also found that a higher tension than the 25 ft-lb spec produced a more consistent board width with less blade wander, so my torque wrench is set at 29.  I tried the 7 degree Woodmizer turbo blades recently in some frozen wood, I will be buying more.

I was wondering about the blade weld as I've seen the cross cut marks (#3 pattern all down the board) even with a new blade.  The #3 pattern cross marks compress or expand with the speed I was sawing, so a bad tooth set makes sense.  

Though I prefer smooth cuts, for some reason people I saw for want to see saw marks, the worse they are the more they like it.  They see 'character' where I see 'bad sawmiling' that will require more planing.  I'll keep some blades with bent teeth around so I can saw bad boards when needed.

Yellowhammer - thanks for the insight on the 'washboard' pattern.  Yes, that's from sawing too slow.  I've seen it come back where I had to slow down for a knot, or something that caused me to stop and restart a cut.

I'm also suspicious of drive belt tension, and sawdust and pitch build up.  I'd just finished two days of cutting up pine.  I clear out the sawdust, but it constantly builds up behind the belt tensioner.  I'm also still on the original drive belt, which has some nicks from a mis-aligned blade change that came off on the backside of the drive wheel.  Time to change the belt, the blade, and read the saw marks on some fresh wood.

Thanks everyone for the advice.  
HM130 with extended 18' trailer + boat winch, homemade log arch, oak ramps, cant hook and lots of leverage.

WV Sawmiller

  I have read here where people kept or deliberately knocked the set off a blade to increase the lines. I think in one case a guy wanted the lines for increased traction on some stair treads he was sawing. I have seen Marty Parsons deliberately slow down his sawing at demos to show the increase in the lines. They would not show on normal rapid sawing but slowing down the feed rate would cause them to appear.
Howard Green
WM LT35HDG25(2015) , 2011 4WD F150 Ford Lariat PU, Kawasaki 650 ATV, Stihl 440 Chainsaw, homemade logging arch (w/custom built rear log dolly), JD 750 w/4' wide Bushhog brand FEL

Dad always said "You can shear a sheep a bunch of times but you can only skin him once

Chuck White

It doesn't matter what degree band you use, you'll get that initial washboard angled result occasionally when sawing too slow, try adjusting your feed speed! 

I use 10° band exclusively and sometimes I get both of those marks, and adjust accordingly!

The pattern after the washboard is usually caused by one (or a few) teeth with to much set, could have hit something on the previous cut!
~Chuck~  Cooks Cat Claw sharpener and single tooth setter.  2018 Chevy Silverado and 2021 Subaru Ascent.
With basic mechanical skills and the ability to read you can maintain a Woodmizer  LT40!

moodnacreek

I was hired to resaw  mahogany boxes to put a circle saw tooth finish on 4 sides. These where going to a foundry to be cast in bronze. First I had to do samples. The artist was very concerned about the saw marks. What I did was start in slow and keep it at that feed. They came out uniform and I got paid well.

RAYAR

Watch your drive belt while cutting, if it's flopping about, then it needs to be tightened up. A belt that is flopping around will usually give you that washboard effect. It should be running smoothly.
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